Human mutations affect the epigenetic/bookmarking function of HNF1B.

Bookmarking factors are transcriptional regulators involved in the mitotic transmission of epigenetic information via their ability to remain associated with mitotic chromatin. The mechanisms through which bookmarking factors bind to mitotic chromatin remain poorly understood. HNF1ß is a bookmarking transcription factor that is frequently mutated in patients suffering from renal multicystic dysplasia and diabetes. Here, we show that HNF1ß bookmarking activity is impaired by naturally occurring mutations found in patients. Interestingly, this defect in HNF1ß mitotic chromatin association is rescued by an abrupt decrease in temperature. The rapid relocalization to mitotic chromatin is reversible and driven by a specific switch in DNA-binding ability of HNF1ß mutants. Furthermore, we demonstrate that importin-ß is involved in the maintenance of the mitotic retention of HNF1ß, suggesting a functional link between the nuclear import system and the mitotic localization/translocation of bookmarking factors. Altogether, our studies have disclosed novel aspects on the mechanisms and the genetic programs that account for the mitotic association of HNF1ß, a bookmarking factor that plays crucial roles in the epigenetic transmission of information through the cell cycle.

Hepatocyte Nuclear Factor-1ß Controls Mitochondrial Respiration in Renal Tubular Cells.

AKI is a frequent condition that involves renal microcirculation impairment, infiltration of inflammatory cells with local production of proinflammatory cytokines, and subsequent epithelial disorders and mitochondrial dysfunction. Peroxisome proliferator-activated receptor γ coactivator 1-α (PPARGC1A), a coactivator of the transcription factor PPAR-γ that controls mitochondrial biogenesis and function, has a pivotal role in the early dysfunction of the proximal tubule and the subsequent renal repair. Here, we evaluated the potential role of hepatocyte nuclear factor-1ß (HNF-1ß) in regulating PPARGC1A expression in AKI. In mice, endotoxin injection to induce AKI also induced early and transient inflammation and PPARGC1A inhibition, which overlapped with downregulation of the HNF-1ß transcriptional network. In vitro, exposure of proximal tubule cells to the inflammatory cytokines IFN-γ and TNF-α led to inhibition of HNF-1ß transcriptional activity. Moreover, inhibition of HNF-1ß significantly reduced PPARGC1A expression and altered mitochondrial morphology and respiration in proximal tubule cells. Chromatin immunoprecipitation assays and PCR analysis confirmed HNF-1ß binding to the Ppargc1a promoter in mouse kidneys. We also demonstrated downregulation of renal PPARGC1A expression in a patient with an HNF1B germinal mutation. Thus, we propose that HNF-1ß links extracellular inflammatory signals to mitochondrial dysfunction during AKI partly via PPARGC1A signaling. Our findings further strengthen the view of HNF1B-related nephropathy as a mitochondrial disorder in adulthood.

HNF1ß bookmarking involves Topoisomerase 1 activation and DNA topology relaxation in mitotic chromatin.

HNF1ß (HNF1B) is a transcription factor frequently mutated in patients with developmental renal disease. It binds to mitotic chromatin and reactivates gene expression after mitosis, a phenomenon referred to as bookmarking. Using a crosslinking method that circumvents the artifacts of formaldehyde, we demonstrate that HNF1ß remains associated with chromatin in a sequence-specific way in both interphase and mitosis. We identify an HNF1ß-interacting protein, BTBD2, that enables the interaction and activation of Topoisomerase 1 (TOP1) exclusively during mitosis. Our study identifies a shared microhomology domain between HNF1ß and TOP1, where a mutation, found in "maturity onset diabetes of the young" patients, disrupts their interaction. Importantly, HNF1ß recruits TOP1 and induces DNA relaxation around HNF1ß mitotic chromatin sites, elucidating its crucial role in chromatin remodeling and gene reactivation after mitotic exit. These findings shed light on how HNF1ß reactivates target gene expression after mitosis, providing insights into its crucial role in maintenance of cellular identity.

Transcriptional coactivator PGC-1alpha promotes peroxisomal remodeling and biogenesis.

Mitochondria and peroxisomes execute some analogous, nonredundant functions including fatty acid oxidation and detoxification of reactive oxygen species, and, in response to select metabolic cues, undergo rapid remodeling and division. Although these organelles share some components of their division machinery, it is not known whether a common regulator coordinates their remodeling and biogenesis. Here we show that in response to thermogenic stimuli, peroxisomes in brown fat tissue (BAT) undergo selective remodeling and expand in number and demonstrate that ectopic expression of the transcriptional coactivator PGC-1α recapitulates these effects on the peroxisomal compartment, both in vitro and in vivo. Conversely, ß-adrenergic stimulation of PGC-1α(-/-) cells results in blunted induction of peroxisomal gene expression. Surprisingly, PPARα was not required for the induction of critical biogenesis factors, suggesting that PGC-1α orchestrates peroxisomal remodeling through a PPARα-independent mechanism. Our data suggest that PGC-1α is critical to peroxisomal physiology, establishing a role for this factor as a fundamental orchestrator of cellular adaptation to energy demands.

The AMPK-Sirtuin 1-YAP axis is regulated by fluid flow intensity and controls autophagy flux in kidney epithelial cells.

Shear stress generated by urinary fluid flow is an important regulator of renal function. Its dysregulation is observed in various chronic and acute kidney diseases. Previously, we demonstrated that primary cilium-dependent autophagy allows kidney epithelial cells to adapt their metabolism in response to fluid flow. Here, we show that nuclear YAP/TAZ negatively regulates autophagy flux in kidney epithelial cells subjected to fluid flow. This crosstalk is supported by a primary cilium-dependent activation of AMPK and SIRT1, independently of the Hippo pathway. We confirm the relevance of the YAP/TAZ-autophagy molecular dialog in vivo using a zebrafish model of kidney development and a unilateral ureteral obstruction mouse model. In addition, an in vitro assay simulating pathological accelerated flow observed at early stages of chronic kidney disease (CKD) activates YAP, leading to a primary cilium-dependent inhibition of autophagic flux. We confirm this YAP/autophagy relationship in renal biopsies from patients suffering from diabetic kidney disease (DKD), the leading cause of CKD. Our findings demonstrate the importance of YAP/TAZ and autophagy in the translation of fluid flow into cellular and physiological responses. Dysregulation of this pathway is associated with the early onset of CKD.

Low-dose aspirin protective effects are correlated with deregulation of HNF factor expression in the preeclamptic placentas from mice and humans.

Aspirin (acetyl-salicylic acid) is one of the most ancient drugs of the human pharmacopeia. Nonetheless, its action at low doses is not well understood at the molecular level. One of the applications of low-dose aspirin treatment is the prevention of preeclampsia (PE) in patients at risk. Foeto-placental overexpression of the STOX1A transcription factor in mice triggers PE symptoms. Transcriptomic analysis of the placentas, showed that aspirin massively down-regulates genes of the coagulation and complement cascade, as well as genes involved in lipid transport. The genes modified by aspirin treatment are not the ones that are modified by STOX1 overexpression, suggesting that aspirin could act downstream, symptomatically on the preeclamptic disease. Bioinformatics analysis of the promoters of the deregulated genes showed that they are strongly enriched in HNF transcription factors-binding sites, in accordance with existing literature showing their roles as regulators of coagulation. Two of these transcription factors, Hnf1ß and Hnf4α are found down-regulated by aspirin treatment. In parallel, we show that in human patient placentas, aspirin-induced deregulations of genes of the coagulation cascade are also observed. Finally, the expression of Hnf1ß target sequences (Kif12, F2, Hnf4α promoters and a synthetic concatemer of the Hnf1ß-binding site) were investigated by transfection in trophoblast cell models, with or without aspirin treatment and with or without STOX1A overexpression. In this model we observed that STOX1A and aspirin tended to synergize in the down-regulation of Hnf1ß target genes in trophoblasts.

Hepatocyte nuclear factor 1α suppresses steatosis-associated liver cancer by inhibiting PPARγ transcription.

Worldwide epidemics of metabolic diseases, including liver steatosis, are associated with an increased frequency of malignancies, showing the highest positive correlation for liver cancer. The heterogeneity of liver cancer represents a clinical challenge. In liver, the transcription factor PPARγ promotes metabolic adaptations of lipogenesis and aerobic glycolysis under the control of Akt2 activity, but the role of PPARγ in liver tumorigenesis is unknown. Here we have combined preclinical mouse models of liver cancer and genetic studies of a human liver biopsy atlas with the aim of identifying putative therapeutic targets in the context of liver steatosis and cancer. We have revealed a protumoral interaction of Akt2 signaling with hepatocyte nuclear factor 1α (HNF1α) and PPARγ, transcription factors that are master regulators of hepatocyte and adipocyte differentiation, respectively. Akt2 phosphorylates and inhibits HNF1α, thus relieving the suppression of hepatic PPARγ expression and promoting tumorigenesis. Finally, we observed that pharmacological inhibition of PPARγ is therapeutically effective in a preclinical murine model of steatosis-associated liver cancer. Taken together, our studies in humans and mice reveal that Akt2 controls hepatic tumorigenesis through crosstalk between HNF1α and PPARγ.

A suppressor locus for MODY3-diabetes.

Maturity Onset Diabetes of the Young type 3 (MODY3), linked to mutations in the transcription factor HNF1A, is the most prevalent form of monogenic diabetes mellitus. HNF1alpha-deficiency leads to defective insulin secretion via a molecular mechanism that is still not completely understood. Moreover, in MODY3 patients the severity of insulin secretion can be extremely variable even in the same kindred, indicating that modifier genes may control the onset of the disease. With the use of a mouse model for HNF1alpha-deficiency, we show here that specific genetic backgrounds (C3H and CBA) carry a powerful genetic suppressor of diabetes. A genome scan analysis led to the identification of a major suppressor locus on chromosome 3 (Moda1). Moda1 locus contains 11 genes with non-synonymous SNPs that significantly interacts with other loci on chromosomes 4, 11 and 18. Mechanistically, the absence of HNF1alpha in diabetic-prone (sensitive) strains leads to postnatal defective islets growth that is remarkably restored in resistant strains. Our findings are relevant to human genetics since Moda1 is syntenic with a human locus identified by genome wide association studies of fasting glycemia in patients. Most importantly, our results show that a single genetic locus can completely suppress diabetes in Hnf1a-deficiency.

Endoplasmic reticulum stress drives proteinuria-induced kidney lesions via Lipocalin 2.

In chronic kidney disease (CKD), proteinuria results in severe tubulointerstitial lesions, which ultimately lead to end-stage renal disease. Here we identify 4-phenylbutyric acid (PBA), a chemical chaperone already used in humans, as a novel therapeutic strategy capable to counteract the toxic effect of proteinuria. Mechanistically, we show that albumin induces tubular unfolded protein response via cytosolic calcium rise, which leads to tubular apoptosis by Lipocalin 2 (LCN2) modulation through ATF4. Consistent with the key role of LCN2 in CKD progression, Lcn2 gene inactivation decreases ER stress-induced apoptosis, tubulointerstitial lesions and mortality in proteinuric mice. More importantly, the inhibition of this pathway by PBA protects kidneys from morphological and functional degradation in proteinuric mice. These results are relevant to human CKD, as LCN2 is increased in proteinuric patients. In conclusion, our study identifies a therapeutic strategy susceptible to improve the benefit of RAS inhibitors in proteinuria-induced CKD progression.

Clinical and molecular characterization of patients with limb-girdle muscular dystrophy type 2I.

BACKGROUND: Limb-girdle muscular dystrophy type 2I is caused by mutations in the fukutin-related protein gene (FKRP). FKRP encodes a putative glycosyltransferase protein that is involved in alpha-dystroglycan glycosylation. OBJECTIVES: To identify patients with limb-girdle muscular dystrophy type 2I and to derive genotype-phenotype correlations. DESIGN: Two hundred fourteen patients who showed muscle histopathologic features consistent with muscular dystrophy or myopathy of unknown etiology were studied. The entire 1.5-kilobase FKRP coding sequence from patient DNA was analyzed using denaturing high-performance liquid chromatography of overlapping polymerase chain reaction products, followed by direct sequencing of heteroduplexes. RESULTS: Thirteen patients with limb-girdle muscular dystrophy type 2I (6% of all patients tested) were identified by FKRP mutation analysis, and 7 additional patients were identified by family screening. Six missense mutations (1 novel) were identified. The 826C>A nucleotide change was a common mutation, present in 35% of the mutated chromosomes. Clinical presentations included asymptomatic hyperCKemia, severe early-onset muscular dystrophy, and mild late-onset muscular dystrophy. Dilated cardiomyopathy and ventilatory impairment were frequent features. Significant intrafamilial and interfamilial clinical variability was observed. CONCLUSIONS: FKRP mutations are a frequent cause of limb-girdle muscular dystrophies. The degree of respiratory and cardiac insufficiency in patients did not correlate with the severity of muscle involvement. The finding of 2 asymptomatic patients with FKRP mutations suggests that modulating factors may ameliorate the clinical phenotype.

Screening for ryanodine receptor type 2 mutations in families with effort-induced polymorphic ventricular arrhythmias and sudden death: early diagnosis of asymptomatic carriers.

OBJECTIVES: We sought to establish the role of genetic screening for ryanodine receptor type 2 (RyR2) gene mutations in families with effort-induced polymorphic ventricular arrhythmia (PVA), syncope and juvenile sudden death. BACKGROUND: The RyR2 mutations have been associated with PVA, syncope and sudden death in response to physical or emotional stress. METHODS: We studied 81 subjects (39 males and 42 females; mean age 31 +/- 20 years) belonging to eight families with pathogenic RyR2 mutations. All subjects underwent screening for RyR2 mutations, electrocardiography (ECG), 24-h Holter monitoring, signal-averaged electrocardiography (SAECG), two-dimensional echocardiography and exercise stress testing. Electrophysiologic (EP) study was performed in nine patients. RESULTS: Six different RyR2 mutations were found in eight families. Forty-three family members carried the gene mutation. Of these, 28 (65%) showed effort-induced arrhythmic symptoms or signs and one died suddenly during follow-up. Family history revealed 19 juvenile cases of sudden death during effort or emotion. In two families sharing the same mutation, no subject presented with PVA during the stress test; thus, sudden death and syncope were the only clinical manifestations. The 12-lead ECG was normal in all but two subjects, whereas five patients showed positive late potentials on the SAECG. In 17 (39.5%) of 43 subjects, the two-dimensional echocardiogram revealed localized kinetic abnormalities and mild structural alterations of the right ventricle. The EP study was not able to induce PVA. CONCLUSIONS: The absence of symptoms and PVA on the stress test in more than one-third of carriers of RyR2 mutations, as well as the lack of PVA inducibility by the EP study, underlies the importance of genetic screening for the early diagnosis of asymptomatic carriers and prevention of sudden death.

Juvenile sudden death in a family with polymorphic ventricular arrhythmias caused by a novel RyR2 gene mutation: evidence of specific morphological substrates.

We report on a family with a history of sudden death and effort-induced polymorphic ventricular arrhythmias. The index case was a 17-year-old boy who died suddenly and at postmortem had evidence of fibrofatty replacement in the right ventricular free wall, consistent with arrhythmogenic right ventricular cardiomyopathy, as well as calcium phosphate deposits within the myocytes. A molecular genetics investigation carried out in the paraffin-embedded myocardium of the subject and in blood samples of family members disclosed a missense mutation in exon 3 (230C-->T; A77V) of the cardiac ryanodine receptor type 2 gene. The carriers showed effort-induced polymorphic ventricular tachycardia in the setting of normal resting electrocardiogram and trivial echocardiographic abnormalities, consistent with catecholaminergic polymorphic ventricular tachycardia. The observation of both arrhythmogenic right ventricular cardiomyopathy type 2 and catecholaminergic polymorphic ventricular tachycardia in the same family suggests that the two entities might correspond to different degrees of phenotypic expression of the same disease. This experience underscores the importance of a precise autopsy diagnosis in the case of sudden cardiac death, including molecular genetics, and the mission of pathologists to guide further clinical investigation of family members.

Celastrol Protects against Obesity and Metabolic Dysfunction through Activation of a HSF1-PGC1α Transcriptional Axis.

Altering the balance between energy intake and expenditure is a potential strategy for treating obesity and metabolic syndrome. Nonetheless, despite years of progress in identifying diverse molecular targets, biological-based therapies are limited. Here we demonstrate that heat shock factor 1 (HSF1) regulates energy expenditure through activation of a PGC1α-dependent metabolic program in adipose tissues and muscle. Genetic modulation of HSF1 levels altered white fat remodeling and thermogenesis, and pharmacological activation of HSF1 via celastrol was associated with enhanced energy expenditure, increased mitochondrial function in fat and muscle and protection against obesity, insulin resistance, and hepatic steatosis during high-fat diet regimens. The beneficial metabolic changes elicited by celastrol were abrogated in HSF1 knockout mice. Overall, our findings identify the temperature sensor HSF1 as a regulator of energy metabolism and demonstrate that augmenting HSF1 via celastrol represents a possible therapeutic strategy to treat obesity and its myriad metabolic consequences.

Serum- and glucocorticoid-inducible kinase 1 (SGK1) regulates adipocyte differentiation via forkhead box O1.

The serum and glucocorticoid-inducible kinase 1 (SGK1) is an inducible kinase the physiological function of which has been characterized primarily in the kidney. Here we show that SGK1 is expressed in white adipose tissue and that its levels are induced in the conversion of preadipocytes into fat cells. Adipocyte differentiation is significantly diminished via small interfering RNA inhibition of endogenous SGK1 expression, whereas ectopic expression of SGK1 in mesenchymal precursor cells promotes adipogenesis. The SGK1-mediated phenotypic effects on differentiation parallel changes in the mRNA levels for critical regulators and markers of adipogenesis, such as peroxisome proliferator-activated receptor gamma, CCAAT enhancer binding protein alpha, and fatty acid binding protein aP2. We demonstrate that SGK1 affects differentiation by direct phosphorylation of Foxo1, thereby changing its cellular localization from the nucleus to the cytosol. In addition we show that SGK1-/- cells are unable to relocalize Foxo1 to the cytosol in response to dexamethasone. Together these results show that SGK1 influences adipocyte differentiation by regulating Foxo1 phosphorylation and reveal a potentially important function for this kinase in the control of fat mass and function.

The binding of the RyR2 calcium channel to its gating protein FKBP12.6 is oppositely affected by ARVD2 and VTSIP mutations.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy type 2 (ARVD2, OMIM 600996) and stress-induced polymorphic ventricular tachycardia (VTSIP, OMIM 604772) are two cardiac diseases causing juvenile sudden death, both associated with mutations in the RyR2 calcium channel. By using a quantitative yeast two-hybrid system, we show that VTSIP- and ARVD2-associated point mutations influence positively and negatively, respectively, the binding of RyR2 to its gating protein FKBP12.6. These findings suggest that ARVD2 mutations increase RyR2-mediated calcium release to cytoplasm, while VTSIP mutations do not affect significantly cytosolic calcium levels, thereby explaining the clinical differences between the two diseases. The present two-hybrid system appears to be an efficient molecular tool to assay the binding of FKBP12s proteins to both cardiac RyR2 and skeletal muscle RyR1 isoforms, circumventing the full-length expression of this class of giant channels. We also provide evidence of the suitability of this system to test new drugs that target RyRs-FKBP12s interactions and do not affect yeast growth.

Denaturing HPLC-based approach for detecting RYR2 mutations involved in malignant arrhythmias.

BACKGROUND: Mutations in the RYR2 gene, which encodes the cardiac ryanodine receptor, have been reported in patients showing either arrhythmogenic right ventricular cardiomyopathy, type 2, or stress-induced polymorphic ventricular tachycardia. Both clinical phenotypes are characterized by a high risk of sudden death. Detection of RYR2 mutations is particularly important because beta-blocker treatment has been shown to be effective in preventing fatal arrhythmias in affected patients. METHODS: We used denaturing HPLC (DHPLC) to identify mutations in the human RYR2 gene. Fifty-three single exons, possibly targeted by mutations, were identified by comparison with the distribution of pathogenic mutations of the RYR1 gene, the skeletal muscle counterpart of RYR2. PCR primers for amplification of the entire coding sequence (116 amplicons, corresponding to 105 exons) were tested, and optimal DHPLC conditions were established. DHPLC analysis of critical exons was performed on 22 unrelated patients with effort-induced polymorphic ventricular arrhythmias but lacking a precise diagnosis. RESULTS: We identified four novel missense mutations among 22 patients. Their pathogenic role was related to present knowledge of the structure and function of RyR2 protein. CONCLUSIONS: Under optimized conditions, DHPLC is a cost-effective, highly sensitive, rapid, and efficient method for mutation screenings. A four-step approach is proposed for mutation screening of the RYR2 gene: (a) DHPLC analysis of 48 critical exons (2-4, 6-15, 17-20, 39-49, 83, 84, 87-97, and 99-105); (b) DNA sequencing of 5 critical exons unsuitable for DHPLC; then, in case of negative results, (c) DHPLC analysis of the remaining 39 exons and (d) DNA sequencing of the last 13 amplicons unsuitable for DHPLC analysis.